Ion-producing mechanism for calutrons



Sept. 13, 1966 A. M- VEACH ETAL ION-PRODUCING MECHANISM FOR CALUTRONS Filed Jan. 10, 1964 INVENTORS. Allen M. Veach BY Oliver C. Yon ls ATTORNEY.

United States Patent 3,272,983 ION-PRODUCING MECHANISM FOR CALUTRONS Allen M. Veach and Oliver C. Yonts, Oak Ridge, Tenn.,

assignors to the United States of America as represented by the United States Atomic Energy Commission Filed Jan. 10, 1964, Ser. No. 337,112 1 Claim. (Cl. 250-419) The present invention relates to ion-producing mechanisms, and more particularly to an improved ion-producing mechanism for the electro-magnetically operated equipment known as calutrons for the separation of isotopes or elements.

It has been shown that isotopes of many chemical elements can be separated and the desired elements enrichcd in the electromagnetic mass spectrometer known as the calutron, described in the E. 0. Lawrence patent, No. 2,709,222. In the calutron, as described in this patent, there is provided an ion-producing means wherein a feed or charge material is converted into ions for subsequent acceleration through a magnetic field and separation into the respective masses of the isotopes present in the charge material. Since most charge materials are solids, the charge must first be heated in a vaporizer or oven to produce a charge vapor. Vapor from the vaporizer or oven passes to an arc chamber where a stream of electrons (commonly called the arc) is passed through these vapors, ionizing them for subsequent acceleration.

The disadvantages of the calutrons used in the prior art have been set forth in the application of William A. Bell, Jr., et al., Serial No. 149,131, filed October 31, 1961, now Patent No. 3,115,575, issued December 24, 1963. The above disadvantages have been, in most respects, overcome by the calutron described in the above application. However, the device of the above application still has the disadvantage of undesirable high pressures in the accelerating region of the ion source, and the disadvantage in that un-ionized material is deposited on the face of the unit and the electrods thereof which leads to arcing and other disruptions that adversely affect the focus of the ion beam and thus are detrimental in the separation of isotopes. The present application is an improvement over the aforementioned prior application.

With a knowlerge of the disadvantages of all prior calutrons, it is a primary object of the present invention to provide an ion-producing mechanism of unitized construction for calutrons that substantially eliminates the high pressures in the accelerating region of the mechanism.

It is another object of this invention to provide an ionproducing mechanism for calutrons that includes means for drawing off and collecting any un-ionized material from the mechanism during operation.

It is a further object of this invention to provide an ion-producing mechanism that can be more conveniently handled when toxic, chemically reactive, or radioactive charge materials are utilized.

Other objects and advantages of the present invention will become apparent from the following detailed description and the accompanying drawing in which:

The single figure is a cross-section of the unitized enclosure of the ion-producing mechanism of the present invention.

The above objects have been accomplished in the present invention by modifying the arc chamber section of the above prior application, in the manner to be described below, and in providing a divergent channel communication with the arc chamber section for substantially reducing the pressure in the acceleration region and for 3,272,983 Patented Sept. 13, 1966 collecting any un-ionized material fom the arc chamber section as set forth below.

As in the above-mentioned Patent No. 3,115,575 and in the present invention, the ion-producing mechanism is formed in a single, unitized structure with the oven section and the arc chamber section combined into one composite enclosure. This unitized enclosure is preassembled and then inserted in the remainder of the calutron source unit. A water-cooled support bracket, not shown, provides the necessary alignment of the enclosure with respect to the cathode filament, magnetic field, and accelerating electrodes in the same manner as set forth in the above-mentioned application.

Between the oven section and the ionization or are chamber section of the unitized enclosure is provided a vapor passageway for transmitting vapors from the oven section to the arc chamber section. The oven section of the present invention is the same as that set forth in the above-mentioned application and comprises a large central cavity for the accommodation of a charge bottle and heaters adjacent to two sides of the charge bottle within the cavity for vaporizing the charge material in the charge bottle. The are chamber section of the enclosure of the present invention has been modified over that shown in the above-mentioned application and comprises a central cavity which is divided by a perforated baflle into two regions, a vapor manifold region with inlet passageways for the vapors from the oven section and an ionizing region for ionization of the vapors. A heater cavity with a heater disposed therein is disposed adjacent to the ionizing region. In addition, a heated battle is disposed within the ionizing region for more effectively directing the feed vapor into the electron beam directly behind the ion exit slit. The small channel between the heated bathe and the ion exit plate is in communication with a divergent channel and a bottom-vented chamber for the withdrawal of un-ionized feed vapor in a manner to be described below. Ions from the ionizing region pass through an exit slit and are accelerated through the magnetic field of the calutron to a collection receiver in a well known manner.

In order to control the temperature gradient in the enclosure and between the two sections of the enclosures, thermal insulation is provided. In the oven section, thermal insulation consisting of graphite sheets is disposed on all sides and both ends of the charge bottle. In the arc chamber section, thermal insulation is disposed in the heater cavity between the walls of the cavity and the heater. By using more or less thermal insulation, it is possible to vary the temperature of the different sections of the enclosure. For higher internal temperature, more insulation is used, and for lower temperatures, less insulation is needed. Also, it is usually necessary to maintain the arc chamber section at a higher temperature than the oven section to prevent solidification of vapors entering the vapor manifold region. This temperature gradient can be maintained and controlled by varying the amount of thermal insulation, such as graphite, disposed between the two sections.

With reference to the drawing, the unitized enclosure is preferably divided into two sections, an arc chamber section 8 for ionization of the vapors from the charge bottle and an oven sect-ion 1 for heating and vaporizing the charge material to be ionized. These two sections may be machined separately from graphite blocks and bolted together to form the unitized enclosure for the ionproducing mechanism.

The oven section 1 of the enclosure is machined with a large central U-shap-ed cavity 27 of rectangular cross section designed to accommodate a -boX-like charge bottle -2 for the heating and vaporization of charge material.

This charge bottle 2 which is machined from graphite or stainless steel, depending upon the type of charge material to be vaporized and the temperature required, is provided with a covered opening for insertion of charge material and at least two exits to accept the threaded vapor-exit nipples 6, only one of which is shown. Carbon heaters 3, 4 in suitable ceramic supporting insulators 28, 29 are disposed adjacent to two sides of the charge bottle 2 within the large central cavity 27 with appropriate terminals 20, 20' aflixed to the ends of heaters 3,4 extending through slots communicating with the rear of the cavity 27. Thermal insulation is provided first by members 21, 22 and 23 machined preferably from carbon. Thermal insulation may be further provided by a multiplicity of thin carbon or graphite sheets 5 disposed on all sides within the cavity 27. The thermal insulation 5 adjacent to the arc chamber section 8 is drilled to accommodate the vapor-exit nipples 6 which extend from the charge bottle 2 to the vapor manifold region of the arc chamber section.

The arc chamber section 8 is provided with a longitudinal cavity 11 for the ionization of the charge vapors and which is provided with a perforated graphite bailie 25. This baffle 25 extends the length of the cavity 11 and separates the arc chamber section into two regions, the ionizing region and the vapor manifold region 7. The baffle 25 is provided with a plurality of openings 12, only one of which is shown. The cavity '11 is bounded on the front by a slotted graphite insert 33 defining an ion exit slit 13.

The vapor manifold region 7 is provided with at least two drilled holes or vapor inlets to accommodate the vapor-exit nipples 6 extending from the charge bottle 2. The are chamber section 8 also contains a heater cavity 30. A carbon heater 9 in a ceramic supporting insulator 31 and with appropriate terminals is inserted from the open end of the cavity 30. Thermal insulation in the form of a multiplicity of thin carbon sheets 10 is inserted, as shown, between the heater 9 and the cavity 30. A face plate 26 is used to retain these components in the heater cavity 30.

Disposed within the ionizing region of the arc chamber section is a baflie 14 so as to direct feed vapor into a narrow channel 34 which directs the feed vapor more elfectively into an electron beam or are discharge directly behind the ion exit slit 13. The structure for providing the electron beam and its operation is set forth in the above-mentioned Patent No. 3,115,575, to which reference is made. In order to provide sufficient heat for the ionization region, another heater 15 surrounded by a ceramic insulator 32 is disposed within the baffle 14.

The lower portion of the arc chamber section 8 is removed to provide a generally divergent channel 16 for the withdrawal of any un-ionized feed vapor from the narrow channel 34. The channel 16 discharges into a bottom-vented chamber 17. The chamber 17 is provided with a plurality of water-cooled baffles 18 to achieve condensation of the surplus un-ionized feed vapor, and the lower portion of the surfaces of the chamber 17 are also cooled for this purpose. Cooling is provided by water tubes 19 joined to the surfaces, as shown. The dimensions of the above vapor withdrawal system are not critical. Although not shown, provision may be made for revaporizing the deposited material in chamber 17 and recycling it to the arc chamber section so that the chamber 17 would then essentially serve as a second charge bottle.

The heaters described for use in both sections of the ion-producing mechanism are machined from carbon or graphite, preferably in a zig-zag pattern, to provide the proper electrical resistance and optimum heater surface area for the particular element or isotope to be vaporized. Details of the heater design for the oven section are shown in detail in the above-mentioned Patent No. 3,115,575, to which reference is made. The electrical connections to heaters 9 and 15 of the arc chamber section may be made in the same manner in which the electrical connections are made to the arc chamber heaters in the above-mentioned application.

In operation of the above-described ion-producing mechanism, the charge material is placed in the charge bottle 2, which is tightly covered to prevent leakage into the oven section. The unitized enclosure is assembled, as described above, with the two sections 1 and 8 bolted together and then the chamber '17 is afiixed thereto in any conventional manner. When the two sections 1 and 8 are connected, the vapor-exit nipples 6 from the charge bottle 2 extend into the vapor manifold region 7, and to prevent vapor leakage back into the oven section 1, threaded graphite nuts 24 are used to secure the vaporexit nipples 6. The assembled unitized enclosure is then inserted within a calutron source unit, in a water-cooled support bracket as in the above-mentioned Patent No. 3,115,575, which provides the necessary alignment of the enclosure with respect to the magnetic field and accelcrating electrodes. After the heater terminals are connected to a suitable power source, the calutron is operated in essentially the standard manner as described in the Lawrence patent. First an arc is struck through the arc chamber and passes through the narrow channel 34, using a support gas, such as nitrogen, for the arc. The charge material is then vaporized in the oven section and these vapors eventually support the arc and are substantially ionized for subsequent acceleration in the standard manner.

The above-described ion-producing mechanism has been operated for the production of a calcium ion beam, for example. The ion beam routinely contained about 30% of the material evaporated in the mechanism, and about of the remaining material was trapped in the chamber 17 and on the baffies 18. Thus, only 34% of the total charge material passed out through the accelerating electrode region in un-ionize-d form. This improvement over the prior art is very important. For example, many charge materials are costly because of their scarcity. If unused portions of the charge material are scattered over a considerable area of the calutron unit, as in the past, recovery operations are lengthy and expensive and often result in high loss rates. Furthermore, if the material is dangerous to handle, as in the caseof plutonium, this recovery process is especially difficult. With the unused feed material largely concentrated, as in the present invention, within the chamber 17, many of these problems are minimized.

Another advantage which is attained with the present invention is the elimination of undesirable high pressures in the accelerating region of the ion source, which is accomplished by use of the vented bottom chamber 17 in communication with the arc chamber section, as described above, which removes the un-ionized charge vapor and thus prevents high pressures from existing in the accelerating region of the ion source. Also, beam blowup occurs often in the prior art due to the above-mentioned high pressures caused by the un-ionized feed vapor if the ion output is raised above what is a normal operating point. By eliminating the high pressures in the accelerating region, as is done in the present invention, the maximum output of the present ion source is about 60% higher than the conventional ion source, and it will operate eificiently at a pressure which is at least an order of magnitude lower than the conventional ion source.

For example, the present ion source will operate efficiently at pressures lower than about 10- mm. Hg.

In addition, the use of the vented chamber 17 in the present invention substantially prevents the deposition of un-ionized material on the face of the unit and the electrodes thereof. In the prior art, the deposition of unionized material on the face of the unit and the electrodes thereof leads to arcing and other disruptions that adversely affect the focus of the ion beam and thus are detrimental in the separation of isotopes. These effects are minimized by the present invention since very little un-ionized material exists in the accelerating region.

This invention has been described by way of illustration rather than by limitation, and it should be apparent that this invention is equally applicable in fields other than those described.

What is claimed is:

In a calutron, an improved ion-producing mechanism comprising a unitized graphite enclosure defining both an arc chamber section and an oven section, said oven section being provided with a large central cavity, a charge bottle adapted to contain .therewithin a charge material, said charge bottle being disposed Within said large cavity, first heaters disposed adjacent to two sides of said charge bottle within said large cavity for heating and vaporizing said charge material, said arc chamber section being provided with a second cavity for the ionization of the vapors from said charge material and at least one heater cavity of rectangular cross section with a second heater disposed therein and in close proximity to said second cavity for supplying heat thereto, said second cavity being subdivided by a perforated bafile into a vapor manifold region and an ionizing region, a slotted graphite insert adjacent to said ionizing region and defining an ion exit slit, said charge bottle being provided with at least two vapor-exit nipples extending therefrom into said vapor manifold region for conveying vapors from said charge bottle directly into said manifold region, a baflle provided with a third heater, said heated baffle being disposed within said ionizing region and defining a narrow channel behind said ion exit slit for directing said feed vapors from said manifold region into the path of an arc discharge passing through said narrow channel for ionizing said feed vapor, a divergent channel and collection chamber communicating directly with said narrow channel, and means for cooling said collection chamber, said chamber being bottom vented by means of a plurality of water cooled baflies, whereby substantially all of said feed vapor which is not ionized by said are discharge is with drawn into said divergent channel and condensed within said cooled chamber thereby essentially eliminating contamiuation of other calutron components from any charge material reactive constituents and also preventing high pressures from existing in the accelerating regions of the calutron unit.

References Cited by the Examiner UNITED STATES PATENTS 2,836,750 5/ 1958 Weimer 250-419 2,967,239 1/1961 Zemany 25041.9 3,115,575 12/ 1963 Bell et al 25041.9

RALPH G. N'ILSON, Primary Examiner.

A. L. BIRCH, Assistant Examiner. 

